1. Field of the Invention
The present invention relates to systems and methods for adjusting seat belt tension of motor vehicle safety systems. More specifically, the invention relates to an anchorage device including a pretensioner for reducing slack in the seat belt prior to and during a vehicle impact.
2. Related Technology
Seat belt restraint systems for automobiles often include a pretensioner as part of a seat belt retractor which applies tension to the seat belt when a vehicle impact or a potential vehicle impact is detected. When activated, the pretensioner eliminates slack in the seat belt, and thus controls the physical space between the occupant and the seat belt. In this manner, less slack is present in the seat belt, thereby controllably restraining the occupant, reducing occupant movement, and controlling loads when the occupant moves forwardly into engagement with the seat belt.
During an impact condition, the vehicle occupant is urged in a forward direction against the seat belt which absorbs energy; potentially causing an undesirable seat belt pay-out. After the pretensioner reduces slack, a locking mechanism is activated to reduce or prevent free webbing pay-out. However, before accomplishing the complete locking, the combination of the pretensioner and the locking mechanism typically allow the belt to travel freely and pay-out a small length of seat belt webbing, a phenomenon commonly known in the art as “locking dip”. Locking dip reduces the degree of coupling between the occupant and the vehicle, which in turn reduces the amount of energy that can be absorbed by the seat belt system during a crash. This leads to higher peak belt forces and higher accelerations experienced by the occupant.
Although current seat belt systems include a pretensioner as part of the seat belt retractor, this configuration may be undesirable for some vehicle designs. For example, the seat belt retractor may not be able to accommodate the pretensioner due to space constraints. Additionally, the location of the retractor within the vehicle seat may be such that the retractor is not conducive to being coupled with a pretensioner. More specifically, the retractor may be mounted in a location that renders maintenance on the pretensioner inconvenient or impractical. Furthermore, due to the presence of several moving components within the seat belt retractor, it may be undesirable to include additional components, such as a pretensioner, that would further increase the complexity of the system.
While current pretensioning devices and methods for pretensioning a vehicle seat belt achieve their intended purpose, many enhancements and additional features are needed. Therefore, a new and improved pretensioning system and method for reducing locking dip would be desirable.